web: provide the file number to the diffstat templates

This allows the diffstat templates to link into the diff output. For example,
the URLs of the first three files within the diff are #l1.1, #l2.1, #l3.1.

mercurial/hgweb/webutil.py

@@ -223,10 +223,12 b' def diffstat(tmpl, ctx, parity):'
             return 0
         return (float(i) / maxtotal) * 100
 
+    fileno = 0
     for filename, adds, removes, isbinary in stats:
         template = filename in files and 'diffstatlink' or 'diffstatnolink'
         total = adds + removes
-        yield tmpl(template, node=ctx.hex(), file=filename,
+        fileno += 1
+        yield tmpl(template, node=ctx.hex(), file=filename, fileno=fileno,
                    total=total, addpct=pct(adds), removepct=pct(removes),
                    parity=parity.next())